Marmots will be prepared surgically with chronic catheters, renal artery flow probes and impedance electrodes to determine: 1. Seasonal glucose tubular maximum. 2. The biological half lives of cortisol and aldosterone during normothermia and hibernation. 3. Fractional blood flow to the kidney. 4. The extraction ratio of para-aminohippurate in the unanesthetized normothermic and hibernating animal. 5. Cardiac output, arterial pressure and and peripheral resistance in normothermic and hibernating conditions. 6. Maximum ability to concentrate urine.